The present invention relates to a scroll fluid machine used both as a compressor and a vacuum pump for a nitrogen generator and a medical oxygen concentrator.
To concentrate a gas such as nitrogen or oxygen contained in air at room temperature, there are a film-separation method, a PSA method using adsorbent and a method of using oxygen adsorbent (CMS). The film-separation method comprises the steps of pressing air by a compressor, transferring it into a hollow film and simultaneously depressurizing the hollow film by a vacuum pump at an outlet of or on the hollow film.
To concentrate oxygen using a nitrogen adsorbent such as zeolite by an adsorbent-applying PSA method, air taken from the atmosphere is pressurized and forwarded into an absorption tower, in which nitrogen that passes in air is adsorbed, and oxygen-rich air is discharged from an outlet of the adsorption tower. When nitrogen is not adsorbed in the adsorption tower, a path between the upstream and the compressor of the adsorption tower is closed to allow the downstream to communicate with a vacuum pump, by which the adsorption tower is depressurized and adsorbed nitrogen is desorbed to return as exhaust gas to air.
To concentrate oxygen using oxygen adsorbent, air taken from atmosphere is pressurized by a compressor and forwarded into an adsorption tower, in which oxygen in air that passes is adsorbed, and air from which oxygen is removed is discharged from an outlet of the adsorption tower and returned as exhaust gas to air.
When oxygen is adsorbed in the adsorption tower, a path between the upstream of the adsorption tower and the compressor is closed to allow the downstream to communicate with a vacuum pump and the adsorption tower is depressurized by the vacuum pump, so that adsorbed oxygen is desorbed to discharge oxygen-rich air.
In both of the methods, the compressor and vacuum pump are necessary.
In the foregoing, a separate compressor and a separate vacuum pump are provided, and a large space is required to dispose them. It is difficult to locate them in a small area and its transportation is inconvenient to involve increase in cost of transportation.
To solve the disadvantages, the inventors invented a scroll fluid machine having both functions of a compressor and a vacuum pump to enable it to use in a small space and to be transported easily, as disclosed in U.S. Pat. No. 6,709,248.
FIGS. 1 and 2 of the appended drawings illustrate a scroll fluid machine that has a fixed scroll 3 having a spiral fixed wrap 2 on a fixed end plate 1, and an orbiting scroll 7 having a spiral orbiting wrap 6 on an orbiting end plate 5 to form a sealed compressing chamber between the fixed wrap 2 and the orbiting wrap 6, the orbiting scroll 7 being eccentrically revolved on a driving shaft 4, the compressing chamber being separated into an outer compressing chamber “A” and an inner compressing chamber “B” by an annular partition wall 8 of the fixed scroll 3 or the orbiting scroll 7, the outer compressing chamber “A” having an outer inlet 9 and an outer outlet 10 for compressing and discharging a gas sucked through the outer inlet 9, the inner compressing chamber “B” having an inner inlet 11 and an inner outlet 12 for discharging a gas sucked through the inner inlet 11.
At the end of the orbiting wrap 6, a known tip seal 6a is fitted to be in sliding contact with the fixed end plate 1 suitably.
A bearing plate 13 is provided behind the orbiting scroll 7 to rotate together with the scroll 7 and has a bearing tube 14 at the back of the bearing plate 13. A bearing 15 is fitted in the bearing tube 14 to support an eccentric portion 4a of a driving shaft 4 rotatably.
In operation, the outer compressing chamber “A” is operated as a vacuum pump, while the inner compressing chamber “B” is operated as a compressor.
In the scroll fluid machine, during operation, difference occurs in pressure between the outer compressing chamber “A” and the inner compressing chamber “B”. Thus, the inner portion of the orbiting end plate 5 is subjected to higher thrust in a direction such that it moves away from the fixed end plate 1, compared with the outer portion.
Hence, the orbiting end plate 5 is partially distorted or deformed, and contact pressure of the tip seal 6a to the fixed end plate 1 is partially variable thereby causing a gap between the fixed plate 1 and the tip seal 6a of the inner orbiting wrap 6.
With deformation of the orbiting end plate 5, the bearing plate 13 behind the orbiting scroll 7 is deformed or distorted, thereby acting excessive thrust or inclining force to the bearing tube 14 for the bearing 15 that rotatably supports the eccentric portion 4a of the driving shaft 4, which results in decrease in durability of the bearing 15 and generating excessive heat.